Relay Installation for a Marine Alarm / Horn Rated Over 100 mA

Some marine horns and lamps are rated to draw more than 100 mA. By itself, the alarm pin on a Garmin® chartplotter or sounder will not work with a horn and/or lamp rated above 100 mA.

Installing a relay allows the alarm pin to control an external device that draws much more current, such as a 100W lightbulb, without damaging the alarm pin. The alarm pin is attached to the low-current “energizing coil” side of the relay, and the horn and/or lamp is attached to the high-current “contact switch” side of the relay. When the “energizing coil” is activated by the alarm pin, the “contact switch” closes to turn on the horn and/or lamp.

See the chartplotter or sounder's installation manual for more information on installing a horn or light.